That may sound intimidatingly Olympian, but it’s not. On the contrary, it’s surprisingly easy—and fun. “The buoyancy of water lessens the pull of gravity, making you feel lighter and making balance simple, while also reducing impact on your knees,” says personal trainer and Prevention contributing editor Chris Freytag, who created this routine. “This makes the same moves that would be difficult to do on land feel easier in the pool.” The payoff is powerful: This workout blasts calories, tones trouble spots, and boosts muscle strength—in less than 30 minutes. We tested our Hydro Belly-Blaster routine on a group of real women wearing heart-rate monitors. On average, the women burned 318 calories in 28 minutes. Katie Kerrigan, 35, torched a whopping 363 calories. “I just had my third baby, and lifting weights in my living room feels too hard,” Kerrigan says. “I really enjoyed this routine. I felt like I could move my body much easier in the water, and it kept me cool.” Do this workout 5 times a week and cut your daily diet by 250 calories, and you’ll be 8 pounds slimmer by the end of summer. What You’ll Need

A pool where you can stand in chest-deep waterA resistance band; our testers used a SPRI red Xertube ($15; spri.com)A waterproof watch, timer, or heart-rate monitor to time sets

How To Do It

Start with a 2-minute warm-up of treading water or easy swimming.Do each Hydro Belly Blaster strength circuit twice.Between each Hydro Belly-Blaster circuit, do 1 minute each of your Fat-Zapping Cardio Moves.Cool down with 2 minutes of full-body stretching.

Total workout time: 28 minutes CIRCUIT 1 HYDRO BELLY BLASTER

  1. Tick-Tock With Upright Row Targets: Legs, shoulders, upper back, absMedia Platforms Design Team Stand on band with both feet, right handle in left hand and left handle in right hand (a). Lift right leg out to side, pulling handles toward shoulders (b). Return to start, and repeat with opposite leg. Continue alternating legs for 1 minute to complete 1 set.2. Squats To Overhead Shoulder Press Targets: Legs, butt, shoulders, abs(a)(b) Stand on band with both feet slightly more than shoulder-width apart, holding one handle in each hand. Squat as though sitting down in an imaginary chair, keeping knees behind toes . Pause; stand up, pressing hands overhead . Repeat for 1 minute to complete 1 set. MORE: 10 Moves That Target Cellulite CIRCUIT 2HYDRO BELLY BLASTER3. Chest Fly Targets: Chest, shoulders, abs(a)(b)4. Overhead Pull With Knee Lift Targets: Arms, shoulders, back, abs, legs Stand with right foot 2 to 3 feet in front of left foot, left foot on top of band, holding handles at chest level with elbows bent . Press handles forward, extending arms in front of chest . Return to start, and continue for 1 minute to complete 1 set.(a) (b) MORE: 50 Things You Must Do This Summer CIRCUIT 3HYDRO BELLY BLASTER5. Knee Tuck Targets: Abs, butt(a)(b)6. Leg Sweep Targets Legs, butt, abs Stand 2 feet away from side of pool, feet hip-width apart and hands resting on wall. Draw left knee into chest, rounding back and contracting abs . Extend leg behind you, squeezing through glutes . Continue for 30 seconds. Switch legs, and repeat for 30 seconds to complete 1 set. MORE: Tone Your Butt Without A Single Squat Or Lunge FAT-ZAPPING CARDIO MOVES Water RunMedia Platforms Design Team Keeping abdominals tight, run from one side of pool to the other. Swing arms powerfully through water and lift knees high toward chest. Continue for 1 minute to complete 1 set.Power Pop-UpMedia Platforms Design Team Stand with feet hip-width apart. Lower into a squat, keeping knees behind toes. Then jump, raising arms overhead and lifting feet off pool floor. Land softly in squat position, knees bent. Continue for 1 minute to complete 1 set. 3 Ways To Boost Your Calorie Burn1. Contract Your CoreBefore beginning each move, tighten your abs to keep your balance in the water. Maintain this contraction throughout the exercise, but breathe normally.2. Watch Your FormMove quickly to amp up heart rate-the more reps you do in each set, the more calories you’ll burn—but don’t go so fast that you lose control of the movement.3. Trim With TunesBlasting fast-paced pool grooves from your iPod will motivate you to push harder. Keep your iPod safe with water-proof speakers, such as the Eco Extreme Rugged All Terrain Speaker Case ($35, amazon.com).  TONE-UP TOOLS FOR THE POOL Take your water workout further with this get-wet gearMedia Platforms Design TeamPolar FT4 ($100, polarusa.com) This water-resistant watch lets you time yourself in the pool while tracking heart rate and calorie burn.Media Platforms Design TeamRyka Aqua Fit 4 ($65, ryka.com) These made-to-be-submerged sneakers are superlight and quick-drying. Plus, they offer ankle support and no-slip safety during your workout.Media Platforms Design TeamHand Buoys ($33 per pair, spri.com) Beef up your workout with foam barbells. When submerged, they pack 2.5 to 9 pounds of force, depending on size.Media Platforms Design TeamElite Fitness Gloves ($15, amazon.com) These webbed gloves close the space between fingers, making muscles work harder when hands cut through water.   MORE: 6 Signs You Definitely Shouldn’t Swim There